Generally, in feedback control systems, information from feedback sensors is used to measure and ultimately control a system's output parameters or control signals. Difficulty arises in converting the feedback signal into an electrical or digital format when a system is required to support high resolution, i.e., how fine the measurement is, over a large range of operation, i.e., the possible range of the measurements. One solution to this problem is to use multiple sensors having outputs tailored to cover different ranges within the total measurement range. Each sensor is then provided with sufficient resolution within the designated range.
Alternatively, another solution is to pass the output of a single sensor through multiple amplifiers, where each amplifier is designed to operate only within a designated range of the total measurement range. Again, each amplifier is arranged to provide sufficient resolution within the designated range. While either solution can achieve the desired resolution and large size of measurement range, neither solution is able to transition smoothly between the multiple feedback sources or ranges.
For example, in either situation, i.e., a single sensor having a feedback signal processed into multiple gains, or multiple sensors having different gains, a sensor (or gain) is selected by a control process based on a desire to use a feedback signal within the associated range or gain. In this situation, the control process will continue to use the output signal from the selected range as long as the output signal remains below a particular threshold value. If the output signal exceeds the threshold value, the control process switches to processing the output signal associated with an adjacent range or gain.
The problem encountered with such an arrangement results from any mismatch or “error” between the two signals when transitioning between the two ranges. This is particularly true if the two ranges have a different resolution. In such a situation, the control process is likely to respond to the error between the transitioned to value and the actual measured value of the second range by generating a “bump” or “glitch” in the controller output. Such bumps or glitches are generally not acceptable where accuracy is desired in the control process.
Therefore, a need exists for an arrangement that can process multiple feedback signals of different range in such a manner as to produce a smooth, or seamless, transition between the different ranges.